Fluid mixer



Sept. 24, 1968 J. A. VAN INGEN ETAL FLUID MIXER Filed NOV. 1, 1967 JOHNC M FALL JACK A. V 'UNGEN INVENTORS A onrs United States Patent3,402,917 FLUID MIXER Jack A. Van Ingen, Webster, and John C. McFall,Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., acorporation of New Jersey Filed Nov. 1, 1967, Ser. No. 679,695

11 Claims. (Cl. 259-7) ABSTRACT OF THE DISCLOSURE A fluid mixer whichblends two or more viscous fluids without substantial hold-up time inthe mixing chamber having an impeller with at least two axially spacedblades. At least one stationary blade extends radially inwardly from themixing chamber housing bet-Ween the blades of the impeller. Each of theimpeller blades has a pitch which varies from near the axis of theimpeller to the outer tip of the blade.

Background of the invention Many processes require the intimate andcomplete mixing of two or more materials and many types of mixingapparatus have been devised in order to accomplish the specificrequirements of various processes. It is known that, in mixing togetherfluids of high viscosity, it is desirable to create high. shear forceswithin the fluids in order to overcome their viscous nature and permitintimate mixing. Normally, the process of mix-ing together two or moreviscous fluids has utilized a mixer incorporating screw-type blades,paddles, pairs of meshing gears rotating in a housing, or one of manyother forms of agitators well known in the art.

Mixing apparatus of the prior art includes the batchtype wherein aselectedquantity ofthe various fluids to be mixedare introduced into alarge mixing chamber and the mixer agitator is operated until thedesired degreeof mixing is achieved. Other forms of mixers include thein-line type, wherein only a very small volume of fluid is contained inthe mixer at any one time and .the fluid is constantly dischargedtherefrom so that there is little or nohold-up time of the mixed fluidswithin the mixingchamber. Each of these types of mixing operations havetheir respective advantages and disadvantages.

Batch-type mixers, having relatively low speeds and extended mixingtimes, are employed when complete mixing of the components is necessarywith very little probability of entraining air in the fluid. However,many processes cannot employ such a batch-type mixing operation due tothe fact that various characteristics of the mixed fluid change afterthe components are combined so that prolonged hold-up in a mixingchamber undesirably changes the characteristics of the mixed fluid.Examples of such systems are those utilizing chemical reactions whereinthe reaction commences as soon as the elements are brought together andthe mixed fluid proceeds to lose its eflicieucy or desirablecharacteristics with prolonged hold-up.

In-line mixers are used in systems such as the foregoing in an attemptto overcome the problems of extended fluid hold-up in the mixingchamber. Such in-line mixers maybe either of the pump type, or of thefixed orifice type wherein the fluids are passed through an orifice toan expansion chamber. In pump type in-line mixers, problems areencountered ,at high operation speeds due to the fact that cavitation ofthe fluid results at the pump agitator. In many operations suchcavitation is intolerable due to the fact that entrained air isintroduced into the fluid which may later negatively affect the qualityof the final product. In an attempt to utilize pump-type mixers at highproduction rates, defbub'bling apparatus has been emice ployed betweenthe outlet of the mixer and the point of fluid application. However, thede-bubbling apparatus generally introduces a substantial hold-up time tothe fluid, resulting in the characteristic change problems noted above.

Orifice-type mixers are generally subject to the same problems as thepump-type mixers, with the additional consideration that highthroughputs result in excessively high pressure drops and the problemsassociated therewith.

As a result, it has become increasingly apparent that a mixer capable ofthoroughly mixing viscous fluids without introducing entraining airtherein and which can be disposed in the system just prior to theutilization of the mixed fluid would be extremely desirable.

Summary of the invention Accordingly, the present invention provides anin-line mixer which can thoroughly mix two or more viscous liquids atsubstantially greater production rates than has been heretofore possiblewithout generating bubbles or entraining gas in the fluids. Furthermore,the present invention provides a mixer which will thoroughly mix theviscous fluids without requiring a substantially hold-up time in themixer whereby the fluids can be quickly used after the initial mixing.

More specifically, the present invention provides a mixer comprising asubstantially cylindrical housing having an inlet opening substantiallyradially therein. An outlet from the housing is angularly displacedabout the periphery of the mixer housing from the inlet. An impeller isdisposed coaxially within the housing and has at least two axiallyspaced blades, each of which have a pitch which varies from the axis ofthe impeller to the outer tip of the blade. At least one stationaryblade is disposed within the mixer housing and extends inwardly from theinner surface thereof between the axially spaced blades of the impeller.

Furthermore, the mixer of the present invention is provided with animpeller having at least two sets of blades, with one set of bladesbeing axially spaced from the other set, and with the roots of all ofthe impeller blades lying in a common diametral plane of the impeller.

Moreover, the mixer of the present invention is arranged so that thetips of one set of impeller blades lead the roots thereof and the tipsof the other set of blades trail the roots thereof.

Also, the blades of the impeller of the present invention are arrangedso that the pitch of the blades having the leading tips is arranged todirect fluid toward the blades having the trailing tips, and the pitchof the blades having the trailing tips is arranged to direct the fluidaway from the blades having the leading tips.

The various features of novelty which characterize the present inventionare pointed out with particularity in the claims annexed to and forminga part of this specification. For a better understanding of theinvention, its operating advantages and the specific objects obtained byits use, reference should be had to the accompanying drawings anddescriptive matter in which the preferred embodiments of the presentinvention are illustrated and described.

Brief description of the drawings FIG. 1 is a plan view of a preferredembodiment of the mixer of the present invention, with the upper sidethereof removed;

FIG. 2 is an elevation view of the mixer of the present invention takenalong line 22 of FIG. 1; and

FIG. 3 is an elevation view of a preferred embodiment of an impeller ofthe present invention.

Description of the preferred embodiment The preferred embodiment of thepresent invention is illustrated in FIGS. 1 through 3, and comprises asubstantially cylindrical housing having circular end walls 12 and 14.One end wall, 12 can be provided with an axial opening therethrough anda bearing 16 to accommodate a drive shaft 18. The opposite end 14 of thehousing may be boltably connected to the cylindrical housing 10 and maybe provided with an O-ring seal 20, in a manner well known in the art. Aplurality of inlet connections 22 extend radially inward through thecylinder wall 10 of the housing and an outlet 24 extends radiallyoutward from the cylinder wall of the housing. As shown in FIG. 2, theinlets and outlet are substantially axially central of the housing. Therelative spacing of the inlets and the outlet will be more thoroughlydescribed hereinafter.

An impeller, generally indicated at 26, is disposed coaxially within thehousing 10 and comprises a central hub 28 arranged to be fixed to theend of the drive shaft 18 in a manner well kown in the art. The impelleris rotated by a power source (not shown) through drive shaft 18 in thedirection of arrow 36. The impeller is provided with at least twoaxially spaced blades and, as shown in the preferred embodiment, twosets of axially spaced blades, 30 and 32, which extend substantiallyradially outward from the hub to close proximity of the inner surface ofthe housing 10. In the preferred embodiment each set of blades consistsof a pair of blades extending from opposite sides of the hub. Morespecifically, all of the impeller blades may be arranged so that theroots thereof all lie in a common diametral plane of the hub,substantially as shown. Each of the blades 30 and 32 curves from theroot, or point where it joins the hub 28, to the tip. The blade angle;i.e., the angle produced between a line tangent to the blade tip and aline connecting the blade tip with the axis of the impeller, is between30 and 45. Each of the leading and trailing surfaces of the impellerblades 30 and 32 has a pitch which varies from a maximum at the root ofthe blade to a minimum at the tip of the blade. A plurality ofstationary blades 34 are connected to the inner periphery of housing 10and extend radially inward therefrom between the two pairs of impellerblades 30 and 32. As will be seen in FIG. 2, the stationary blades 34are disposed in the space between the two sets of impeller blades.

It has been found that the specific configuration of the impellerblades, in cooperation with the stationary blades extending inwardlyfrom the housing, produce the desired high-speed uniform mixing ofviscous fluids without undesirable cavitation. Specifically, theimpeller blades of I the preferred embodiment of the present inventionare arranged so that the tips of one set of blades 30 lead the rootsthereof, and the tips of the other set of blades 32 trail the rootsthereof. The leading and trailing surfaces of each blade have a pitchwhich decreases from the root to the tip. The pitch of the blades havingthe leading tips 30 is such that fluid is directed therefrom paststationary blades 34 toward the opposite blades 32. At the same time,the pitch of the blades 32 having the trailing tips is arranged todirect fluid away from blades 30.

Furthermore, the end walls, 12 and 14, are arranged to be substantiallycontiguous to the impeller 26 to minimize the mixing chamber volume, andthus the fluid hold-up time, and also to improve the blendingcapabilities of the mixer. Moreover, it has been found that lesscavitation or air entrainment is encountered with the present mixer whenit provides no pumping action to the mixed fluids.

Another feature which is important to the successful operation of thepresent invention is the arrangement of inlets 22 downstream, in thedirection of impeller movement, from the outlet 24. It has been foundthat it is necessary to locate the inlets with an angle of approximately270 measured from the outlet in the direction of movement of theimpeller. Moreover, it has been found that mixing of fluids havinghigher viscosities requires that the inlets be placed within a smallerangle than the foregoing.

A specific example of a mixer of the present invention is one having aninside diameter of approximately 4 inches and a depth of 2 inches, witha capacity of approximately 0.5 pound of fluid. The inner surface of themixing chamber is provided with a Teflonf lining. This mixer, driven ata speed of 1800 rpm. by a one horsepower motor, successfully mixed amultiple component solution having a viscosity of 400 centipoises withsubstantially no bubble generation at a throughput of 8 to 10 timesgreater than that possible with gear-type mixers of the prior art.

While the preferred embodiment illustrates two sets of blades eachhaving two blades, it will be appreciated that an impeller having setsof blades, each having three or four blades, could be employed.

The present invention provides a mixer arrangement which generates acombined axial and radial flow pattern wherein the fluid being mixed isforced outward toward the blade tip and the stationary blades withincreasing velocity as it moves toward the periphery of the blade. Thestationary blades appear to help eliminate cavitation problems andcreate complex turbulent flow within the mixing fluid.

Accordingly, the present invention provides a mixer capable of blendingviscous fluids at relatively high production rates with minimal airentrainment from cavitation of the fluid at the impeller. As a result,the present mixer may be utilized in-line directly before utilization ofthe mixed fluid with little or no hold-up so that the quality of themixed fluid is optimized.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention as described hereinabove and as defined in the appendedclaims.

We claim:

1. A mixer comprising a substantially cylindrical housing, an inletopening substantially radially into said housing, an outlet angularlydisplaced from said inlet and opening substantially radially outwardlyfrom said housing, an impeller disposed coaxially within said housingand having at least two axially spaced blades, each of said impellerblades having a pitch varying from near the axis of the impeller to theouter tip of the blade, a stationary blade connected to the innersurface of said housing and extending radially inward between theaxially spaced blades of said impeller, and means for rotating saidimpeller about its axis within said housing.

2. The invention according to claim 1 wherein the inlet and outlet openinto said housing between said axially spaced impeller blades.

3. The invention according to claim 1 wherein the impeller comprises atleast two sets of blades extending radially therefrom with one set ofblades being axially spaced from the other set.

4. The invention according to claim 3 wherein the roots of all impellerblades lie in a common diametral plane of the impeller.

5. The invention according to claim 3 wherein the tips of one set ofimpeller blades lead the roots thereof and the tips of the other set ofblades trail the roots thereof.

6. The invention according to claim 5 wherein the pitch of the bladeshaving leading tips is arranged to direct fluid toward the blades havingthe trailing tips, and the pitch of the blades having the trailing tipsis arranged to direct fluid away from the blades having the leadingtips.

7. A mixer comprising a substantially cylindrical housing forming asubstantially cylindrical mixing chamber, an impeller disposed coaxiallywithin said'housing and having at least two axially spaced sets ofblades, each of said impeller blades having a pitch varying from theaxis of the impeller to the outer tip of the blade, an inletopeningsubstantially radially into said housing between th axially spacedblades of said impeller, an outlet angularly displaced from said inletand opening substantially radially outwardly from said housing betweenthe axially spaced blades of said impeller, a stationary blade connectedto the inner surface of said housing and extending radially inwardbetween the axially spaced blades of said impeller, and means forrotating said impeller about its axis within said housing.

8. A mixer comprising a substantially cylindrical housing forming asubstantially cylindrical mixing chamber, an impeller disposed coaxiallywithin said housing and comprising a hub having at least two sets ofblades radiating therefrom, one set of blades being axially spaced fromthe other set of blades, the tips of one set of blades leading the rootsthereof and the tips of the other set of blades trailing the rootstheref, the leading and trailing surfaces of each blade having a pitchwhich decreases from the root to the tip, the pitch of the blades havingthe leading tips arranged to direct fluid toward the blades having thetrailing tips, and the pitch of the blades having the trailing tipsarranged to direct fluid away from the blades having the leading tips, aplurality of inlets opening substantially radially into said housingbetween the axially spaced blades of said impeller, an outlet angularlydisplaced from said inlet and opening substantially radially outwardlyfrom said housing between the axially spaced blades of said impeller, aplurality of stationary blades connected to the inner surface of saidhousing and extending radially inward between the axially spaced sets ofblades of said impeller, and means for rotating said impeller about itsaxis within said housing, said inlets opening through the cylindricalhousing into said mixing chamber within an angle of 270 measured fromthe outlet in the direction of movement of said impeller.

9. The inventtion according to claim 8 wherein the inlets and the outletare disposed substantially axially centrally of said mixing chamber.

10. The invention according to claim 8 wherein each set of bladesconsists of a pair of blades each of which extend from opposite sides ofthe hub.

11. The invention according to claim 10 wherein the roots of all bladeslie in a common diametral plane of the hub.

References Cited UNITED STATES PATENTS 2,538,466 1/1951 Marco 2599WILLIAM I. PRICE, Primary Examiner.

JOHN M. BELL, Assistant Examiner.

